At present, methods for reading-out panels of photostimulable phospors (also called storage phosphors) are based on scanning the panel with a laser beam. The beam, focused onto a scanning plane containing the phosphor panel, is moved back and forth along the scanning line while the panel translates in a direction perpendicular to the scanning line.
Light emitted point by point by the panel is collected by optical means and transferred to a photodetector which produces corresponding electrical signals. The electrical signals are amplified, filtered and sampled according a suitable means (e.g., a clock) fixing the distance between adjacent points. This information is than stored in a computer memory.
Reading-out methods of this type are described, for example, in EP-A-0077677 and EP-A-0051460.
The use of such reading-out methods for reading-out structured phosphor panels does not give satisfactory results. In fact, it may happen that the sampled signal that is emitted corresponding to the center of the cell (wherein the output is maximum), or that emitted corresponding to the border of the cell (wherein the output is minimum), or even that signal read as emitted corresponding to the inert substrate (wherein the output is obviously null). The image formation therefore can be highly altered. Moreover, interference phenomena may seriously damage the image quality.
To obviate these problems, it is theoretically possible to spatially synchronize the sampling. However, that procedure is highly difficult to realize in practice, due to the disuniform speed with which the laser beam runs along the scanning line.